If you ever copied hundreds or even thousands of files from one folder to the other with both folders containing files of the same name you might have realized that there is a button missing when transferring those files. Windows asks the user what he would like to do when a duplicate file is found in the folder where he is copying the files into.
The user has the option to say Yes, Yes to all, No or Cancel. There is one option missing and that is No to all. If you do not want to replace files in the destination folder you have to click on No for every duplicate file. If you copy thousands of files this could be a lot. Is there another option ? Yes there is.
I really like Windows because it has so many hidden features. That's sarcasm by the way. It would have been much easier if the button No to all would be available. To select the option you have to press the SHIFT key and then click on No. This has the effect that future duplicate files will not be copied to the destination folder and will not replace the files that are already in that folder.